Existing 2G and 3G cellular systems such as Global System for Mobile Communications (GSM) and Universal Mobile Telephone System (UMTS) operate over a frequency band which is relatively narrow compared to the frequency of operation—for example, the UMTS system has an operating band extending from 1920 to 2170 MHz. The design of antennas offering good performance with bandwidths for one or more 2G or 3G systems is relatively well established.
Future wireless systems, such as 4G or what is commonly referred to as Long Term Evolution (LTE), will require much higher data transfer rates than existing systems, and as a result the required operating bands will become wider. The UWB systems defined by the WiMedia Alliance and the IEEE 802.15 standards describe systems with operating bands ranging from 3.1 to 10.6 GHz. At the same time, the long term evolution of wireless handsets and terminals will see an increased functionality and the capability to operate on multiple systems so that the physical dimensions of the constituent parts of each system will become necessarily smaller. For such future systems, a new type of antenna design becomes an imperative: an antenna which retains the small physical dimensions of antennas for 2G and 3G systems while offering good performance over a bandwidth extending over several GHz.
Wideband planar antennas are well known, for example U.S. Pat. No. 5,828,340, Johnson, describes a planar antenna having a 40% operational bandwidth, where the extended bandwidth is achieved by forming a tab antenna on a substrate where the tab antenna has a trapezoidal shape. Furthermore, it is known that the physical dimensions of an antenna can be reduced by fabricating the antenna on a substrate with a high dielectric constant, such as Alumina. U.S. Pat. No. 7,019,698, Miyoshi, describes a gap-fed chip antenna comprising a radiating portion formed by the union of a reversed triangular portion and a semicircular portion sandwiched between two dielectric layers and comprising a feeding portion which couples to the radiating portion. The antenna taught by Miyoshi is suitable for use as an antenna device operating according to the UWB system and has dimensions in the order of one quarter of one wavelength at an operating frequency of 6 GHz. A similar antenna is described in U.S. Pat. No. 7,081,859, Miyoshi et al.
FIG. 1 of the accompanying drawings shows a prior art monopole chip antenna comprising a dielectric chip 10, arranged on an insulating carrier substrate 15. The antenna includes a radiating element 11 fabricated on an upper surface of dielectric chip 10, a feed point, realized by a metal input/output (I/O) pad 12 fabricated on the lower surface of dielectric chip 10, a metal connecting trace 16A connecting the I/O pad 12 to radiating element 11. Carrier substrate 15 includes a feed line 17 which connects a transceiver device (not shown) to metal I/O pad 22 and a ground plane 13 offset from dielectric chip 10.
Despite the advances taught in Johnson and Miyoshi, for integration in mobile wireless handsets and terminals, antennas with further reduced physical dimensions are highly desirable. Moreover a solution to the problem of producing a highly miniaturized ultra wideband antenna with excellent performance characteristics (e.g. a return loss of less than −6 dB and a high radiation efficiency over a frequency range from 3.1 to 10.6 GHz) has, so far, yet to be found.
Accordingly, it would be desirable to provide a wideband chip antenna fabricated on a dielectric substrate, which is suitable for integration in a portable wireless handset or terminal, where the bandwidth of the antenna extends over an ultra wide band frequency range, e.g. from 3.1-10.6 GHz, and where the antenna has dimensions which are small compared with the wavelength of the lower edge of the operating frequency band of the antenna.